The present invention relates to a method that utilizes electromagnetic waves for locating underground anomalies of high electrical contrast, and more particularly it relates to the use of electromagnetic waves transmitted between adjacent boreholes to detect an anomaly therebetween by diffraction of the waves at the edges of the anomaly.
In general, prior electromagnetic methods for detecting underground anomalies have the advantages of rapidity of survey, portability of equipment and minimal destructiveness of the environment. However, these methods are surface electromagnetic methods and have been found to be insensitive for detecting anomalies of high electrical contrast at depths of more than six or seven diameters of the anomaly. Thus, heretofore, no electromagnetic method has been adequate for surveying for such anomalies on sites for large structures such as large buildings, dams and nuclear reactors, or for searching for abandoned tunnels in old mines such as in preparation for reactivating the mine.